twin reverb silverface 135 mod...again:)

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by analogica, Feb 17, 2009.

  1. analogica

    analogica Member

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    Hi guys,

    hello everyone,a newbie around here...

    Im another lucky owner...., I have a 135 silverface and I want to change the tone a bit, I play an 75 ibanez strato and it sounds super brighty and metallic.

    I just want to make the sound a bit softer, but I dunno where to begin, theres some kits around there but Im not sure if it is what I need.

    Ill change my fender speakers for some webers (do u like them???) and
    a cabinet with 4 x 12" is too much ??? 2 x 12" is enough???

    Ive made some diy proyects, pedals and mic pres, but I have more respect for the valves....I dont wanna fry myself, If I do not touch the caps enclosure am I safe???

    you will say guys, Im waiting for your advice,

    Thanks everyone....
     
  2. tonemnstr

    tonemnstr Member

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    I worked on one of those over the summer..

    The ultra linear output tranny contributes to that sound. One thing you can do is wire two of the power tubes in false triode mode and just use those or use them in conjunction with the other two. The false triode mode sounds warmer than the ultra linear.

    The other thing is it may have one of those nasty pull boost master volumes...That can either be removed completely and/or wired up with something like a PPIMV.

    If you're going for that blackface sound ultimately you're limited by the output and power trannys. These amps put something like 525V on the plate of the power tubes.....they were built for clean headroom.
     
  3. analogica

    analogica Member

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    thanks tone, more info please....
     
  4. pgissi

    pgissi Member

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    I have owned a 1979 Silverface since 1980, what a mistake this purchase was but having just started playing, I did not know any better. Soon after, I was lucky enough to have access to a 66 Fender Super and the SF sat in the corner lonely but deservedly, what a POS.

    Sterile and shrilll with a high end that could cut diamonds. In time I was able to get a sound out of it with pedals and cab but soon after that I was off to other things with tone. So once again the SF sat.

    Some years later I decided it would be a good platform for experimentation and did not care for any value it may have had, it was somewhat beat up to begin with so I began to operate in the interest of tone.

    disclaimer, this amp will kill you if you dont know what your doing, there is 575VDC on the plates of my amp

    the goal of incarnation #1 was to convert it to a usable master volume style amp with more gain and darker tone
    -converted the bias circuit, undoing the stock the bias balance
    -modded the master volume control
    -removed v1 for more front end gain from chan 2
    -removed the death cap
    -changed some tone and coupling caps
    -retubed, rebiased and experimented with speakers/cabs


    incarnation #2 was to find out if there was a non master volume tone in there that was pleasing and I went further
    -removed the master volume control
    -reduced negative feedback, added a presence control
    -installed voltage switching using zener diodes, preamp and power tubes
    can independently be voltage switched, crazy indeed, running the
    preamp or power section at lower volts browns up the tone
    -retubed, rebiased and experimented with speakers/cabs once again



    Mod 1 was marshall like, with an agressive OD and plenty of power but easily controlled with the PPIMV

    Mod 2 was clean and loud and went into OD only at levels high enough to shake the walls and be useful on the loudest stages but it sang and sustain and howled when there and I thought this was as close to an old BF Twin as this amp will ever get.


    Out of the 2 mods #1 sounded the best since the UL tranny did not complement mod 2 as much and in mod 2 the amp still leaned toward "sounds super brighty and metallic" and required a darker speaker.


    My advice is if you dont have the knowledge and experience to mod this amp to this extent, then its not worth it in addition to being dangerous and if you do, you may still not be satisfied with the result.

    It is what it is

    My SF is still in incarnation 2 and would make a great pedal steel amp, loud, clean and steely!
     
  5. 5er Driver

    5er Driver Member

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    Hell, that's why I bought one! :AOK
     
  6. tonemnstr

    tonemnstr Member

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    I have to agree with pgissi that you'll need to know what you're doing poking around in there........ I also did many of the same things


    -converted the bias circuit, undoing the stock the bias balance
    -installed PPIMV
    -made channel 1 more marshall like and moved the mixer for channels 1&2 back one gain stage
    -reworkd & moved the tone stack in channel 1 further back in the signal path
    -retubed, rebiased
    -reduced negative feedback, added a presence control with resonance

    I ran out of time with the zeners...:(

    What I found is that all the "warming up" I did didn't have as much impact until I got rid of the ultralinear taps on the output tranny. The combination of that and the NFB seemed to have the most dramatic improvement.
     
  7. pgissi

    pgissi Member

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    Spot on, the UL OT with its high voltages are a major contributor to the tone and you cant bias the 6l6 hot enough if you wanted to without smoking them. The volts switching is right out of frakensteins lab and I can run the pre-amp and power stage tubes at high or low volts independently. For the power amp I modified the standby switch to be a DPDT where in the up postion its high volts and down its low volts. For the pre-amp volts selection I installed a switch in the vibrato footswitch hole


    I will tell you where my SF shines, it has clean for days and can do that Lenny tone in spades especially now that its a non master circuit. It also has a nice clean jazz tone but it is still loud and would really make a great pedal steel amp especially as the non master amp it is now.

    When I picked it up way back then it was a mistake simply because it had no OD or it was harsh even with pedals but it always had a clean tone, even in its stock config, was just too hifi like.

    This amp can stun anyone in its path!
     
  8. TweeDLX

    TweeDLX Member

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    There are a lot of simple things you can do to take some of the "edge" off a bright amp. A speaker change will help a lot. Ted Weber is very good at making recommendations for speakers to fit a particular situation. There are also several speakers in the new Eminence line that are "darker" in sound. Go here to see the tone guide: http://www.eminence.com/pdf/tone_guide.pdf . You can also change out tubes, both preamp and power to get a darker tone. Do a search on "tube reviews". If you really want to get inside the chassis, here are some interesting mods (look for the ones titled "Dumble mods"-all done to a Twin):
    http://www.schematicheaven.com/modifications.htm
    FIRST OFF: do a search on "Filter cap draining"!!!

    Mike
     
  9. tonemnstr

    tonemnstr Member

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    Now that is a cool idea...I assume you've strung some zener's end to end on a terminal strip?
     
  10. pgissi

    pgissi Member

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    yes, there is plenty of room in the chassis, I think I found a better way though shown at the bottom of this page to get B+ lower, I may try this in the future-

    Mosfet B+ Reducer
    http://www.geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm
     
  11. analogica

    analogica Member

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    thanks everyone, dont worry i will not try by myself....

    im trying to asimilate your info, lets see:

    pgissi...Can I change the lineal output trafo??? If so, is it better?


    what is the ppimv ??? (sorry im not english)

    what means rebiased ??? adjust the bias ???

    would be nice to change some old caps ????

    ....I want to put 4 webers in a cabinet, what do u think if I put 2 of a model, and 2 different ones...

    thanks guys,
     
  12. TweeDLX

    TweeDLX Member

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    Mike
     
  13. analogica

    analogica Member

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    thanks mike, I know a bit of electronics but so much about tube amps,

    be patience pleaseeeeeeeee

    thanks again
     
  14. davemccarthy707

    davemccarthy707 Member

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    Just change the 250pf treble cap to a 500pf silver mica.
     
  15. RedRock

    RedRock Member

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    Yes, I am patience.
    If you want "a softer sound," try a compressor and/or a pedal EQ. and save a lot
    of money.
     
  16. analogica

    analogica Member

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    Yep, I got a carl martin comp, and a monte allum boss eq is coming....

    I found this article by karates geoff farina:

    MODS USING RESISTORS:

    Here´s a few mods that involve resistors that you can try in your silverface/blackface fender amp.

    2/ CLEANER SOUND:

    Most older fender amps have a 1500 Ohm resistor going from the cathode of the preamp tubes (pin 3 on a 12AX) to ground, in parallel with an electrolytic capacitor.
    Changing this resistor from 1.5K ohms to 2.7K ohms will clean up the tone of your amp and give it less preamp distorsion.

    -Has my 78 silverface that resistor ??? have you try that???

    3/HIGHER FIDELITY:

    you can improve your fender souund by eliminating series resistance of your fender, most fenders have 2 68K resistors that go from the input jacks to the preamp stages of the amp.
    You dont need this unless you are using both channels simultaneously.
    Simply remove them and connect the hot lead( the one that touches the tip of your guitar cable) of the jack you want to use directly to the wire that was soldered to both resistors.

    This puts less garbage in your signal path and improves the clarity of your sound.

    So...it looks not so expensive, maybe with this mods and 4 webers my sound change completely.

    But Mr.Weber said to me that all of the filter caps should be changed, I dunno how many they are and how much each one cost.
     
  17. analogica

    analogica Member

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    Yep, I have a carl martin comp and a boss EQ monte allum is coming, maybe there something brake in my amp...

    I found this article by karates geoff farina:

    MODS USING RESISTORS:

    Heres a few mods that involve resistors that you can try in your silverface/blackface fender amp.

    2/CLEANER SOUND:

    Most older fenders have a 1500 ohm resistor going from the cathote of the preamp tube(pin 3 on 12ax7) to ground,in parallel with an electrolitic cap. Changing this resistor from 1.5K to 2.7K will clean up the tone of your amp and give it less preamp distorsion.

    Do u know if the 135 W silverface have that??? have you try???

    3/HIGHER FIDELITY:

    You can improve your sound by eleiminating series resistance of your fender.
    Most fenders have 2 68K ohm resistors that go from the imput jacks to the preamp stages of the amp.You dont need this unless you´re using both jacks simultaneously.

    Simply remove them and connect the hot lead(the one that touches the tip of your guitar cable)of the jack you want to use directly to the wire that was soldered to both resistors.

    This puts less garbage in your signal path and improves the clarity of your sound.

    It looks not so expensive, isnt it??? maybe with this mods and 4 webers my sound changes a lot.

    Mr.weber said to me yesterday that All of the filter caps should be changed, could you tell how many they are??? and how much would be each one???

    thanks
     
  18. TweeDLX

    TweeDLX Member

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    Spend some time learning to read the schematic http://www.schematicheaven.com/fenderamps/twin_reverb_sf_135_schem.pdf for the amp. There are lots of sites that tell you how to read the symbols. Take some more time and learn a bit about how tube amps work. Have an idea of what you want to achieve with your mods. Try the new speakers first. Then tubes. Then think about digging into the chassis. Better yet, have a tech do it for you. [​IMG]

    Mike
     
  19. tonemnstr

    tonemnstr Member

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    I forgot to ask... what did you use for zeners? I may get that amp back to do some more tweaking on...
     
  20. jgyn

    jgyn Member

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    An easy way to get a less 'spikey' sound from a 135 w twin:

    Turn all tone controls to 0.
    Turn master and pre amp volumes to 10 (with tone controls at 0, there should be no sound).
    Raise tone controls to desired volume.
     

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